This invention related to railway braking systems, specifically braking systems for railway freight trains.
Traditionally, railway freight braking systems have utilized a pneumatic brake system that is both operated by compressed air and in which the control functions are obtained through utilization of pneumatic valves. Prior freight brake systems included the use of a brake pipe or pneumatic communication between the locomotive and each individual car in a freight train. The pneumatic brake pipe was utilized in a multi-function role, including: charging reservoirs on-board each individual freight car; instituting brake application; and controlling the release of the brakes on the train. Such systems generally utilized on-board pneumatic control valves such as ABD, ABDW, ABDX, or DB-60 valves, with 26 TYPE Locomotive brake equipment or Microprocessor with like EPIC sold by Westinghouse Air Brake Company. It was the general practice to use identical functioning pneumatic control valves and related control sequencing on comparably equipped freight cars throughout the train, such that each car's braking sequencing would be similar. Freight cars have varying braking capabilities depending upon the mechanical linkages between the brake cylinder and the brake shoes. In addition, some cars may be equipped from time-to-time with either empty-load or load-sensing equipment which may vary the pneumatic pressure applied to the brakes based upon the specific load or weight of the individual car. The level of desired brake pressure was controlled by the brake pressure in the brake pipe, communicating with the locomotive. The advantages of such prior art system was the utilization of a single pneumatic communication running the length of the train. Some of the desired characteristics in evaluating a freight brake system include the speed with which braking can be initiated on each individual car, the specific value of the braking on each car, regulation of the in-train forces such that the braking is generally shared between cars without excessive pushing or pulling on the couplers connecting the cars, and the accurate regulation of the speed and deceleration of the freight train during overall operation.
It is desirable to limit in-train forces to reduce any damage that might occur to the cargo being carried in each car, and to provide optimum life and reduced maintenance to train equipment.
Current practice often requires that freight cars be utilized over different rail systems such that the specific operating parameters, such as brake pipe operating pressures, may vary from system to system. As a result the same car must be asked to perform over a variety of specific operational parameters, which may differ from the optimum design characteristics for which it was initially built.
Utilization of electrical signals from a locomotive to control brake operation has been utilized in both passenger trains and transit equipment. Typically, an electrical signal is sent the length of the train with the signal level controlling both the propulsion and the desired level of braking. Such electro-pneumatic braking systems are not generally utilized in freight brake operations due to the vastly different requirements between passenger and freight operation. Specifically, trains and transit equipment consist of a few cars, whereas freight trains often operate with 150 or more cars to a single train. Transit and passenger vehicles are typically lighter weight rail vehicles requiring less braking force than a 200 ton freight car. The transit vehicles often operate at very close intervals between stops and therefore seldom reach the high speeds of over-the-road freight trains. In addition, transit vehicles often use electrical dynamic braking where a portion of the braking results from a regenerative or generated electric current on-board each vehicle or pain of vehicle. Freight train braking on the other hand has traditionally relied solely upon frictional braking on each individual freight car. Electro-motive regeneration braking may also be used on freight locomotives that already have electrical motors on-board that vehicle. However, freight cars seldom have electrical propulsion drive motors contained thereon.
It would be highly desirable that freight cars contain a braking system which would optimize the braking of the overall train during their operation over various railroads and various operating parameters. Because the brake equipment on each individual freight car may be designed using different parameters and the operation conditions vary depending upon the brake pipe pressure utilized in different trains and on different railroads, it would be desirable that the freight brake system accommodate such variations under operating conditions.